Opposition finance spokesman Andrew Robb says he has asked the Australian Federal Police to investigate who is responsible for leaking a Treasury document.

Labor and the Coalition are in the midst of a brawl over the credibility of each others' costings.

Earlier in the week a Treasury document that showed an $800 million shortfall in a Coalition savings measure was leaked to Fairfax newspapers.

The Opposition yesterday refused to submit 20 policies to Treasury for costing unless Treasurer Wayne Swan ordered an investigation into the source of the leak.

Mr Robb says he has today contacted the AFP commissioner to request an investigation.

"The Coalition completely rejects the accuracy of this reported analysis," he said.

"This politically motivated leak, 11 days before the federal election, was designed to undermine the credibility of Coalition savings proposals."

Labor has dismissed the Coalition's call for a probe, labelling it as an excuse for not submitting its policies for scrutiny.

But Mr Robb says the policies, including the Coalition's $1.5 billion mental health plan, will not be submitted.

"Considering the way this process has now been compromised, the Coalition reserves the right to withhold policies until such a time that we can be reassured that Treasury is totally impartial," Mr Robb said.

Mr Swan says he will cooperate with any investigation but has accused the Coalition of pulling a stunt.

"The Liberal Party can have an investigation go what every they like but what they're not entitled to do is thumb their nose at charter of budget honesty," he said.

Last year it was sensationally revealed during the OzCar scandal that Treasury official Godwin Grech had been a long-time Liberal mole.

Mr Robb yesterday denied the Coalition's demand for an investigation was hypocritical.

"Look, the fact of the matter is that that person was investigated by the federal police at the instigation of the Government," he said.